以下C#代码中，关于虚方法和抽象方法使用正确的是（） A: publicabstractclassAnimal{publicAnimal(){}}publicabstractvoidRun():Animal{publicCat(){}publicvoidRun(){}} B: publicclassAnimal{publicAnimal(){}}publicabstractvoidRun():Animal{publicCat(){}publicvoidRun(){}} C: publicabstractclassAnimal{publicAnimal(){}publicabstractvoidRun();}publicclasscat:Animal{publicCat(){}publicoverridevoidRun(){}} D: publicvirtualclassAnimal{publicAnimal(){}publicvirtualvoidRun();}publicclasscat:Animal{publicCat(){}publicoverridevoidRun(){}}